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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

Commercial crude anthracene forms masses of yellowish to brown crystalline
scales with an odour resembling that of naphthalene ; according to the degree
of purification, it contains 30-39% of anthracene (English anthracene A con-
tains 40-50%).

Pure anthracene forms white, tabular crystals with a blue fluorescence
m.pt. 216-5°, b.pt. 360° ; it is slightly soluble in alcohol, ether, benzine, carbon
disulphide and cold benzene, and readily soluble in the hot in benzene, pyridine
and glacial acetic acid.

CARBOLIC   ACID

Crude and pure carbolic acid are on the market. The former is of some-
what variable composition, the name being often given to yellowish or dark
brown carbolic oils containing, besides varying quantities of neutral tar
oils, also phenol and its homologues (mainly cresols), whereas it is also
used to designate pale red products rich in phenols and crystallising more
or less easily when cooled. The pure product is colourless or pale red,
crystallisable and soluble in 15 parts of water.

In very impure products the determination of the phenols and neutral
oils is carried out as in 2 ; in the others, the water, solidification point,
and the solubility are determined (3, 4 and 5) and, if required, the quantita-
tive estimation according to Koppeschaar (see 2).

1.  Characteristic Reactions of the Phenols.—The following reactions
are used:

(a)  The aqueous solution of a phenol gives a violet coloration with
dilute ferric chloride solution (provided mineral and organic acids, alcohol,
ether and glycerine are absent).

(b)  When heated gently with a little ammonia and a few drops of sodium
hypochlorite, the aqueous solution of a phenol gives an intensely blue
coloration.

(c)  The substance is shaken with water and the aqueous solution treated
with bromine water: if it is a phenol, a voluminous, white precipitate of
tribromophenol, at first flocculent and afterwards crystalline, is produced.
It is soluble in alkali and is reprecipitated on acidification of the alkaline
solution.   The tribromophenol reaction (Landolt's reaction) is sensitive to
about i part in 44,000.   The cresols and also other organic compounds are
precipitated by bromine water.

(d)  A very sensitive reaction is as follows : About I c.c. of the oil to be
examined is shaken with i c.c. of alcohol, after which 2 c.c. of water and
i c.c. of about i% nitrazole solution (fresh) are added and again shaken :
addition of a little caustic potash then colours the aqueous layer an intense
red in presence of phenols.

2.  Determination of Phenols and Neutral Oils.—The approximate
determination of the phenols and neutral oils in crude phenol may be rapidly
carried out by shaking a measured volume of the sample with double its
volume of 10% sodium hydroxide solution in a stoppered graduated cylinder,
allowing to stand and reading the volume of the neutral oils which separate ;
subtraction of this volume from that of the substance used gives the quantity
of phenols.   To facilitate the separation of the neutral oils it is sometimesrystallised from alcohol in reddish-yellow needles melting at 145°.